Lesson Notes By Weeks and Term v5 - Grade 12

Lesson Video

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Performance objectives

• Explain the causes and consequences of deforestation.
• Discuss the impact and management of alien invasive species.
• Analyse the causes and effects of water pollution and eutrophication.
• Understand the concept of sustainable development.
• Apply knowledge to answer exam-style questions.

Lesson summary

The study of human impact on the environment is crucial for Grade 12 Life Sciences learners, particularly in South Africa. Our country faces significant environmental challenges, from water scarcity and pollution to the impacts of climate change on agriculture and biodiversity. Understanding these issues empowers you to become informed citizens and contribute to sustainable solutions. From load shedding to droughts to the preservation of our unique ecosystems like the Fynbos, this topic is directly relevant to your lives and future. This week, we will delve deeper into specific aspects of human impact and also refine our exam preparation strategies through targeted practice questions.

Lesson notes

2.1 Deforestation: Deforestation is the clearing of forests for other land uses, such as agriculture, urbanization, mining, and infrastructure development. In South Africa, deforestation, although less widespread than in some other regions globally, is significant in certain areas, particularly for agriculture (e.g., sugar cane farming, commercial forestry), fuel wood collection (especially in rural areas), and urban expansion.

Causes: Agriculture: Conversion of forests into agricultural land for crops and livestock grazing.

Fuel Wood Collection: Harvesting trees for firewood, particularly in communities with limited access to alternative energy sources.

Urbanization: Expansion of cities and towns, leading to forest clearing for housing, roads, and other infrastructure.

Mining: Clearing forests for mining operations, including coal mining, which is prominent in South Africa.

Commercial Forestry: While commercial forestry involves planting trees, often monoculture plantations replace natural forests, impacting biodiversity.

Consequences: Loss of Biodiversity: Forests are home to a wide variety of plant and animal species. Deforestation leads to habitat loss and species extinction. South Africa is a biodiversity hotspot, and deforestation threatens many endemic species.

Soil Erosion: Tree roots hold the soil together. Deforestation exposes the soil to wind and rain, leading to erosion and loss of fertile topsoil. This affects agricultural productivity and can cause sedimentation of rivers and dams.

Climate Change: Trees absorb carbon dioxide from the atmosphere during photosynthesis. Deforestation reduces the ability of forests to act as carbon sinks, contributing to increased levels of greenhouse gases in the atmosphere and exacerbating climate change. Burning of cleared vegetation also releases stored carbon into the atmosphere.

Altered Water Cycles: Forests play a crucial role in regulating water cycles. Deforestation can disrupt rainfall patterns, reduce water infiltration into the soil, and increase the risk of floods and droughts.

Reduced Water Quality: Erosion leads to increased sediment in rivers and lakes, which can negatively impact water quality and aquatic life. 2.2 Alien Invasive Species: Alien invasive species are plants, animals, or other organisms that are introduced into an ecosystem outside their natural range and cause harm to the environment, economy, or human health. South Africa is particularly vulnerable to invasive species due to its diverse ecosystems and high levels of endemism.

Examples in South Africa: Plants: Acacia mearnsii (Black Wattle), Eucalyptus species (Gum trees), Hakea species, Lantana camara Animals: Argentine ants, European starling, Feral cats Impacts: Competition with Native Species: Invasive species often outcompete native species for resources such as sunlight, water, and nutrients, leading to a decline in native populations.

Habitat Alteration: Some invasive species can alter the structure and function of ecosystems, such as changing soil chemistry, increasing fire frequency, or reducing water availability. For example, invasive alien plants consume significantly more water than indigenous vegetation, impacting water security in arid and semi-arid regions.

Economic Costs: Managing invasive species can be very expensive, requiring ongoing efforts to control their spread and mitigate their impacts. The Working for Water programme in South Africa is dedicated to clearing invasive alien plants.

Agricultural Impacts: Invasive species can damage crops, reduce yields, and increase the costs of pest control.

Human Health Impacts: Some invasive species can transmit diseases to humans or cause allergic reactions.

Management Strategies: Prevention: Preventing the introduction of new invasive species is the most cost-effective management strategy. This involves strict border controls, quarantine measures, and public awareness campaigns.

Early Detection and Rapid Response: Detecting new infestations of invasive species early and taking rapid action to eradicate them can prevent them from spreading and becoming established.

Control and Eradication: Various methods can be used to control or eradicate invasive species, including mechanical removal (e.g., hand-pulling weeds), chemical control (e.g., herbicides), biological control (e.g., introducing natural enemies), and integrated pest management (IPM).

Rehabilitation: Restoring ecosystems that have been degraded by invasive species is an important part of the management process. 2.3 Water Pollution and Eutrophication: Water pollution occurs when harmful substances contaminate water bodies, such as rivers, lakes, oceans, and groundwater. South Africa faces significant challenges related to water pollution due to industrial activities, agricultural runoff, sewage discharge, and mining operations.